In many industrial applications an elastic ring member such as piston ring or a stop ring which can be fitted into an annular groove of a cylindrical or rod shaped member is necessary. Generally, since the outer diameter of the cylindrical or rod shaped member is greater than the inner diameter of the elastic ring member in its undistorted state, in order to install this type of elastic ring member it must be opened by means of a special tool which is inserted into a gap, or into a pair of specially provided holes formed on either side of the gap, which is formed in a section of the ring shaped member, and held in this expanded condition while the rod member or piston having the annular groove into which the elastic ring member is to be received is inserted into the central hole of the ring member and the ring member is moved to a position of the rod member at which the annular groove is formed. The elastic ring member is then released by the tool and its resilience causes it to contract into the annular groove.
This process has some inconveniences however in that the special tool is required and when installing a great number of the elastic ring members is required, such as in the case of an assembly line, a working must fit the tool into the gap, or into the pair of specially provided holes, of each elastic ring he installs. This is time consuming. Furthermore, if the user accidentally applies too much pressure and expands the ring to far, he runs the risk of permanently deforming or causing the stop ring to become "sprung".